1. Field of the Invention
This invention relates to a halogen free polyolefin material composition, and in particular to a non-halogenated fire resistant plastic pallet that produces a reduced health risk to fire fighters during fires, poses less environmental stress when made and used, offers greater RF transparency for use of electronic devices, allows a lower usage of comparably expensive fire retardant additives, yields a lower weight structure for transport fuel savings and ergonomic handling and is 100% recyclable.
2. Description of Related Art
The wooden pallet is an integral part of North America's distribution system. Wooden pallets are involved in the movement of a significant proportion of all goods bought and sold. The U.S. Forest Service estimated that there were 1.9 billion wooden pallets in America in 1999. Approximately 400 million new pallets are needed each year. One hundred seventy five million of these are pallets repaired for reuse by industry. Therefore, roughly 225 million new wooden pallets enter the supply chain each year.
The Grocery Manufacturers of America (GMA), the largest end-user of traditional 48 inch by 40 inch wooden pallets, have set forth the following specifications for GMA style pallets: (1) exact 48-inch×40-inch dimensions. Square in each direction; (2) true four-way entry that is capable of accommodating existing pallet jacks from all four sides (as opposed to current style with cutouts and stringers); (3) minimum-width pallet jack openings of 12 inches and minimum height of 3¾ inch clearance when under load with the width of each center support being less than six inches to accommodate pallet jacks; (4) smooth, non-skid, top-bearing surface should have at least 85% coverage (with 100% being preferred) and the non-skid surface should be flat with no indentations or protrusions that could cause product damage; (5) bottom-bearing surface of no less than 60% coverage with properly placed cut-outs (12-inches square) for pallet jack wheels from four sides with the surface being flat or having no indentations or protrusions that could cause product damage; (6) all bottom entry edges should be chamfered to ½-inch for easy entry and exit; (7) overall height of platform should not exceed six inches; (8) rackable from both the 48-inch and 40-inch dimensions with an allowable deflection in drive-in and drive through racks of no more than ½ inch; (9) compatible with pallet conveyors, pallet dispensers, skate-wheel pallet-flow racks, and automatic storage and retrieval systems; (10) no protruding fasteners; (11) must be made of material that does not contaminate the product that it carries; (12) must meet or exceed current pallet resistance to fire; (13) must be recyclable (preferably made of recycled material); (14) desired weight under 50 pounds; (15) load capacities of 2,800 pounds and capable of bearing 2,800-pound loads safely in stacks five loads high; (16) repairs should be economically feasible; (17) weather resistant; (18) moisture resistant; and (19) capable of safely moving product, damage free, through the entire distribution channel with multiple cycles (from manufacturer through distributor to retail).
Recently, plastic materials have replaced wood with polyolefins, such as polyethylene and polypropylene, as the primary plastic materials that are used to construct plastic pallets. Polyethylene and polypropylene are among the most widely used plastic materials. Polyethylene and polypropylene provide excellent chemical resistance, easy manufacturability, strength, toughness and durability.
High density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) are the preferred materials within the thermoforming sector of the plastics processing industry because of their relative ease of processiblity compared to polypropylene. Polyethylene grades exhibit heat deflection temperatures between 170° F. and 203° F. Polypropylene is more often a preferred material within the injection molding sector of the plastics processing industry because of its relative ease of processibility in this molding art. Polypropylene is also the preferred material for structural foam molded pallets.
Pallets used in the grocery industry supply chain, for example, including wood pallets, must be 48×40 inches and able to support heavy loads (up to 2,800 pounds) when placed upon warehouse racks with commodities stored thereon. When elevated temperatures exist within the warehouse, the heavy load of the commodity can cause the polyethylene and polypropylene pallets to deflect due to the fact that ordinary warehouse racks only support pallets at their edges. Polyethylene becomes rubbery at temperatures exceeding 120° F. and loses its strength. Polypropylene provides greater stiffness and retains its strength at temperatures up to 150° F. Polyethylene and polypropylene are also the lowest cost commodity grade resins available on the market.
One approach to overcoming heat deflection problems is to add thermosetting resins to the polyolefin base material to provide increase stiffness and load strength. U.S. Patent Application Publication Nos. 2003/0108700 and 2004/0059035 disclose a plastic shipping or storage container having a friction material on the outer surface. The container is formed from a material that has a thermosetting component, a polyolefin component, and a friction layer component. The friction layer component provides the protected surface of the container with a static coefficient of friction of dry or wet surfaces in the range of 0.60 to 1.20, preferably in the range of 0.75 to 1.00, and more preferably in the range of 0.80 to 1.00. For oily surfaces, a desirable container coefficient of friction is in the range of 0.30 to 1.00, preferably in the range of 0.40 to 1.00, and more preferably in the range 0.50 to 0.95. In some embodiments of the invention the container is provided with different coefficients of friction in different locations on the container. The thermosetting component requires a catalyst for curing to form a semi-interpenetrating network.
Most traditional polyolefin resins that include thermosetting components cannot be processed using conventional thermoforming and injection molding techniques. The equipment required to process resins that include thermosetting components, such as the resins disclosed in U.S. Patent Application Publication Nos. 2003/0108700 and 2004/0059035, is not the same as those organized for purely thermoplastic resins. Resins that include thermosetting components can be processed by resin transfer molding, sheet molding compounding, and other similar molding technologies.
Another problem with adding thermosetting resins to a thermoplastic pallet material is that thermosetting resins add weight to the finished product. The additional weight increases transportation costs through increased fuel costs. The additional weight also increases the potential for injury by decreasing the ergonomics of the pallet. Thermosetting resins are also not readily recycled.
Another approach to overcoming heat deflection problems is to add fibers or fillers to the base material to add strength. U.S. Pat. No. 5,143,778 discloses a polyethylene structural material that is reinforced with talc fillers. Fibers and filler can replace rigid cross members.
Another problem with plastic pallets is fire resistance. While wood is inherently combustible and easily ignited, the National Fire Protection Association (of America)(NFPA) has raised concerns about the fire-related risks of plastic pallets. The NFPA promulgated NFPA 231 code standards governing sprinkler systems that suppress fires in warehouses involving wood pallets. The NFPA 231 code standards reduced the severity of fires involving wooden pallets as the source of risk.
The National Association of Fire Marshals, the NFPA, the insurance industry, pallet users, and other members of the fire community have determined that NFPA 231 fire suppression systems are inadequate to suppress the increased heat and combustibility of plastic pallet fires. The fire community replaced NFPA 231 with NFPA 13 in 1999 to distinguish the fire risk of wood and plastic pallets.
The NFPA 13 change allows plastic pallets to be treated like wooden pallets if test data indicates that the burning characteristics of the tested plastic pallets are equal to or better than wood. The Underwriters Laboratory (UL) 2335 and Factory Mutual (FM) 4995 test protocols were subsequently developed to classify plastic pallets that meet NFPA 13. UL 94 5VA is the highest (most flame retardant) UL 94 rating system. A 5VA rating does not insure compliance with UL 2335. Polyethylene and polypropylene overwhelmingly represented the highest portion of the preferred materials for the manufacture of plastic pallets at the time of the NFPA 13 change.
NFPA 13 also places other restrictions on wood pallets and plastic pallets that comply with UL 2335 and FM 4995 standards. For example, it is a code requirement that empty pallets that are stacked together (in “idle storage”) are stored outside the warehouse in order to reduce the fire risk posed by both wood and plastic pallets during idle storage if the sprinkler systems have not been upgraded to particular NFPA standards. These additional code restrictions reduce the over-all efficiency of a smooth flowing distribution operation and add further handling and storage costs. The problem of retrieving pallets from outside in winter with snow on the ground using a fork-lift is a case in point. If a much reduced fire risk pallet was used, the NFPA standards could be modified to allow for the idle storage of low fire risk plastic pallets that have a “lower” rather than “equal” risk with wood to be kept in idle storage inside a warehouse. A low risk plastic pallet is therefore needed to improve the supply chain.
Another small-scale test is set forth in ASTM E1354. The ASTM E1354 test is used by the fire community to pre-test a raw material. This bench-scale test is performed before a potential pallet is submitted for full-scale testing as a pallet according to UL 2335 or FM 4995 test methods. Ordinary polyethylene and polypropylene that are tested according to ASTM E1354 have significantly higher average peak heat release rates than wood. Therefore, the commercial viability of ordinary polyethylene and polypropylene pallets was greatly reduced with the NFPA 13 change.
One approach to reduce the fire related risks associated with polyolefin pallets is to replace the polyolefin materials with other plastics. U.S. Pat. No. 6,784,234 discloses a high performance plastic pallet that utilizes resin compositions that include polyphenylene ether (PPE) homopolymers or copolymers. The PPE resins perform as well or better than wood in UL 2335 testing, typically having an average peak heat release rate of +/−550 kW/m2 with a heat flux of 35 kW/m2. The disclosed PPE resins are highly engineered resins that typically cost more than four times the cost of ordinary polyethylene and polypropylene. The PPE resins are also heavier than ordinary polyethylene or polypropylene. Consequently, PPE resins have not been widely used to make pallets because of expense and weight considerations.
U.S. Patent Application Publication No. 2005/0004281 discloses a high performance plastic pallet. The pallet is manufactured from polyphenylene ether resin, polycarbonate resin, vinyl aromatic graft copolymer resin, polyetherimide resin, or thermosetting resins. The pallet has an open deck design. The pallet is also designed to pass the UL 2335 protocol.
Another approach is to add fire retardants to the polyolefin base material. These additives may be incorporated into an outer coating or into the base material. U.S. Pat. No. 6,758,148 discloses a pallet assembly having at least one pallet member having external surfaces and a flame retardant material affixed to at least one pallet member so as to substantially cover all of the external surfaces of the pallet member. The fire retardant material includes poly-tetrafluoroethylene (PTFE) or teflon.
The introduction of fire retardant additives reduces the processibility of the plastic material having fibers and fillers while adding extra procurement and implementation costs. U.S. Pat. No. 6,998,433 discloses a pallet having up to 30 wt % magnesium hydroxide, 8 wt % alumina trihydrate, 8 wt % zinc borate, and 54 wt % polyolefin resin. The preferred embodiment has 38 wt % of fire retardants. Highly loaded materials (i.e. materials loaded in excess of 45%) have reduced processibility of the base material.
Also, highly loaded materials have a reduced capacity for reinforcing fibers and fillers, which must be replaced by rigid cross members to provide elevated temperature load strength. Rigid cross members add cost and weight to the finished product.
Several halogenated fire retardant packages that a practitioner can blend into a polyethylene or polypropylene resin are commercially available. For example, Faralloy® PE-106 is an extrusion grade, UV resistant, non-blooming flame retardant HDPE supplied by O'Neil Color and Compounding of Garfield, N.J.
Fire resistant additives for polyethylene and polypropylene may also include halogenated organic brominates, chlorinates, phosphates and phosphorus flame retardants. These additives can be used to construct fire resistant pallets having an average peak heat release rate of less than 600 kW/m2 at a heat flux of 35 kW/m3, according to ASTM E 1354. Halogenated materials, however, are known to be dangerous to fire fighters and the environment because they release hazardous gases during fire.
U.S. Pat. No. 6,807,910 discloses a pallet assembly that include halogen based flame retardant resin additives that are added to the polyolefin materials like polyethylene and polypropylene to provide acceptable flame resistance. The plastic pallet can be fabricated from just one type of material.
U.S. Pat. No. 6,955,128 discloses a pallet assembly that includes halogen based flame retardant resin additives. The pallet assembly includes a series of triangular holes on the top surface and a series of ribs on the underside. The structure includes holes that provide a pathway for flames to migrate through the pallet, which can ignite combustible objects or commodities supported upon the pallet. The exposed ribs also increase the surface area of exposure to fire and provide more potential fuel for combustion.
U.S. Pat. No. 6,849,677 discloses a pallet that uses a polyolefin molding resin containing a flame retardant package containing a halogenated organic flame retardant, alumina trihydrate, and antimony trioxide. The flame retardants are supplied as a master batch at a concentration higher than that desired in the pallet, in a polyolefin-compatible polymer. The flame retardant ingredients are incorporated into the polyolefin by conventional techniques. The halogenated fire retardant is tetra-bromobisphenol A (TBBA), a brominated flame retardant having the formula (CH3)2C[C6H2(Br)2OH]2. TBBA and other halogenated precursors are also widely used in the cable and wire industry where PE and PP jackets are provided with fire retardant additives so that the cable and wire casing will not ignite and allow a fire to migrate from room to room.
The disclosed inorganic metals and compounds identified are commercially available in master batch quantity from O'Neil Color and Compounding of Garfield, N.J. The O'Neil Color & Compounding UL Yellow Card for Faralloy® PE-401, has the highest 94-5VA rating.
It is also widely known that antimony trioxide and zinc borate are substantially interchangeable inorganic compounds that act as synergists with hydrated alumina and magnesium and promote lower smoke release rates, as measured in ASTM E1354. Finally, zinc borate would be preferred over antimony for its smoke density fighting proficiency and white smoke coloration.
U.S. Pat. Nos. 5,834,535 and 6,184,269 disclose moldable intumescent compositions that provide a heat or fire barrier to a polyethylene or chlorinated polyethylene base material. An intumescent material is one that undergoes a chemical change when exposed to heat and fire, forming expanding bubbles that harden into a dense, heat insulating multi-cellular char. At the same time that the char is forming, metal oxides release water to wick the fire to provide a fire resistant effect.
The disclosed moldable resin formulations include inorganic water emitting substances (hydrated magnesium, alumina, and intercalated graphite), organic nitrogenous agents that release gases that inhibit combustion (ureas, melamine, cyanurates, and carbonates), smoke suppressants (antimony trioxide and zinc borate), and strengthening fillers (fibers and particles). The composition can be blow molded, injection molded, compression molded or otherwise suitably molded and shaped to a desired geometry or configuration by thermal processes. A small amount of hydrated carbon that is beneficial for the formation of char in a process of intumesence is also disclosed.
The disclosed compositions utilize an organic nitrogenous agent. These nitrogenous agents release gases that inhibit combustion. Nitrogenous agents include ureas, melamine, cyanurates, carbantes and the like. The Abu-Isa formulations provide a two-stage fire suppression effect, whereas the Overholt formulations provide only a single stage fire suppression effect.
U.S. Pat. No. 6,706,793 discloses an intumescent polymer composition. The composition includes a halogenated polymer and an intumescent additive. The intumescent additive includes antimony oxide and intercalated graphite.
U.S. Pat. No. 6,809,129 discloses a moldable elastomeric intumescent material. The material includes chlorinated polyethylene, plasticizers, phosphate based foaming agents, char forming materials, antioxidants, intumescent materials, flame retardant materials, and graphite and/or expandable graphite. The material may also include a curing agent or a co-curing agent.
The materials described therein contain halogenated materials, namely, chlorinated polyethylene, which may generate corrosive HX gases, such as HCl. These toxic by-products are dangerous to persons exposed thereto. Many similar efforts to develop flame retardant systems utilize halogenated components because halogens are very efficient fire retardants. However, because they are environmentally unfriendly, it is desirable to find a fire retardant system that does not use halogens.
U.S. Pat. No. 6,998,433 discloses flame retardant molded polyolefin pallets. The disclosed polyolefin material includes a flame retardant package that includes magnesium hydroxide, alumina trihydrate, and zinc borate. Alumina trihydrate, and its functional hydrated alumina equivalent Al(OH)3, on heating to a critical temperature decomposes into 66% alumina and 34% water. Alumina trihydrate (ATH) has a specific gravity of 2.42 g/cm3. (polyethylene and polypropylene have a specific gravity below one +/−0.95 g/cm3). The disclosed inorganic metals and compounds identified are commercially available in master batch quantity from O'Neil Color and Compounding of Garfield, N.J.
U.S. Patent Application Publication No. 2006/0004134 also discloses flame retardant molded polyolefin pallets. The disclosed polyolefin material includes magnesium hydroxide as the primary fire retardant component.
U.S. Pat. No. 6,228,914 discloses an aqueous intumescent composition that includes a melamine compound, an acidic phosphorous compound, and expandable graphite flake. The graphite flake is present in an amount of from 10 to 60 percent by weight. The disclosed compostion could not be employed in the practice of the present invention because it has a relatively low “onset” intumescent temperature, which means that it will commence exfoliation generally after only a few seconds of exposure to an elevated temperature.
U.S. Patent Application Publication No. 2004/0006164 discloses an intumescent fire retardant polymeric composition. The composition includes a thermoplastic polymer, an intumescent, and a fire-resistant additive. The thermoplastic polymer has less than fifty weight percent of the total composition.
U.S. Pat. No. 5,984,126 discloses a non-metallic industrial container, such as a plastic drum, a fiber drum, composite intermediate bulk container, or other suitable industrial container, having a fire resistant outer layer. The fire resistant outer layer is a thermoplastic polymer filled with intumescent powder. The outer layer is co-extruded onto the structure.
Therefore, a need for light weight, low cost polyethylene and polypropylene pallets having high temperature load bearing strength and fire resistance exists. An additional need exists for a plastic pallet that poses a significantly lower fire risk than wooden pallets. Such pallets provide a significantly lower fire risk than wood that is stored inside a warehouse or wood that is stored on ordinary warehouse racking. Such pallets also achieve lower insurance risk premiums.
Many of the patents and patent applications that are discussed in this section have filing dates that occurred after one or more of the priority dates for the patents and patent applications that are identified in the previous section. Accordingly, the citation and discussion of a patent or patent application in this section should not be construed as an admission that that patent or patent application is a prior art reference.